The communication of powdered, granular, pulverized, or other such material may be complicated by the tendency of such material to stick to portions of a hopper.
Apparatus that induce the flow of material from hoppers include external vibrating devices, internal pulsating air pads that line the hopper walls, mechanically driven rotating agitators, and the like. Rotating agitators generally are impractical on hoppers of relatively large size because moving large masses of powder or granular material may be difficult. Also, while the vibration of the hopper serves to promote the discharge of some materials, vibration may not be effective for materials of a sticky character. Further, hopper rigidity and structural mass may limit the vibration that can be transmitted through the hopper walls and into and through the material contained therein.